1. Field of the Invention
The present invention relates to an image projection apparatus, such as a liquid crystal projector, and more particularly to an image projection apparatus having a cooling mechanism configured to cool the interior of the image projection apparatus by using air.
2. Description of the Related Art
A water-cooling method and a method of using a Peltier element are known as a cooling structure for the image projection apparatus, but many cooling structures use a less expensive air-cooling method that employs a fan than the foregoing methods.
However, the air-cooling method draws into the apparatus the dust from the outside of the apparatus as well as open air due to the fan's drawing force; the dust may adhere to surfaces of a liquid crystal panel (image forming element) or another optical element and appear in a projected image. In general, the image projection apparatus is provided with a dust removing filter at an inlet port for the open air, but a high flow velocity of the drawn air causes an invasion of the dust in the apparatus through the dust removal filter.
In order to prevent the invasion of the dust from the outside, Japanese Patent No. 3,490,024 discloses a method of cooling a heating element, such as a liquid crystal panel, by circulating the air in the apparatus.
However, in the cooling method disclosed in Japanese Patent No. 3,490,024, the air that circulates in the apparatus continuously takes away the heat from the heating element, its temperature rises with the passage of time, and the air cannot maintain a sufficient cooling effect. In this case, the cooling effect can improve by increasing the number of rotations of the fan, but the increased number of rotations of the fan increases the noise generated from the apparatus disadvantageously.